The following relates to the optical, optoelectronic, electro-optical, display, light-switching, light modulation, and related arts.
There are diverse applications for transmissive light switch that is substantially attenuation-free and polarization-independent. One such application is in mobile large-area color displays. The concept is a small, “pocketable” projector unit including a battery-powered projection light source and an image formation device that spatially and temporally modulates light so as to form a large-area display on any available wall or other uniform surface. Development of such devices has been hampered by light attenuation in the optical switching elements due to color filters and polarization-dependent absorption. A projection light source generating white light and using color filters to provide a full color display inherently loses about two-thirds of the input light. Such attenuation is problematic in any projection device, but is especially problematic in a battery-powered pocketable projector because the available optical input intensity is limited by the available battery power.
Color filters can be avoided by using by using three separate projection systems, one for each of the three primary colors (e.g., red, green, and blue). However, the use of separate projection systems increases size and bulk, which is undesirable in a compact projector device.
Color filters can in principle also be avoided by using a field sequential approach in which primary colors (e.g., red, green, and blue) are input sequentially into a single light modulation device at a rate substantially faster than the human eye response. The light modulation device display is modulated in synch with the sequential primary color light inputs so as to generate a rapid succession of corresponding primary color images that are visually perceived as a single full-color image. The intensity of each color component can be modulated using a suitable pulse modulation approach such as pulse width modulation (PWM).
However, in the field sequential approach the same optical switching device processes all the primary color inputs in the temporal sequence, which calls for a wide optical bandwidth switching device having an operational bandwidth encompassing most of the visible spectrum. This is difficult to achieve using a transmission optical switching device. Reflective microelectromechanical system (MEMS) based switching systems can be constructed with nearly 100% reflectivity across the entire visible spectrum. However, reflective light switching devices add substantial complexity to the system and can adversely affect device yield, robustness, and product reliability. Moreover, a reflective optical switch array imposes geometrical limitations on a pocketable projector device, for example making a pen-shaped projector geometry difficult to attain.